A flame retardant is a chemical to be added to a combustible material to make the material hard to burn or to prevent the spread of flames on the material, and has been used in all sorts of materials such as building materials, curtains, rugs, various members for vehicles (such as seat cloth), rubber, plastic, paper, and packaging material. In particular, a technology involving imparting a flame retardant effect to a fiber finds use in a wide variety of applications, and examples thereof include: the use of the flame retardant in textile goods (such as curtains, carpets, and rugs) for places where unspecified number of people gather typified by, for example, theaters, hotels, and high-rise buildings specified in disaster prevention regulations; and the use of the flame retardant in, for example, bedding, baby clothes, clothes for seniors, and the cloth of vehicle seats. Accordingly, there is an extremely high need for a flame retardant for fibers, and hence investigations have heretofore been conducted on flame retardants by many enterprises and organizations.
For example, a flame retardant is generally used in polyester fibers that are produced in large amounts and are frequently used as material for the seat members of vehicles or for curtains, and an alicyclic halogen compound (such as hexabromocyclododecane (HBCD)) has heretofore been a mainstream flame retardant. The compound brings together excellent flame retardant effects and durability. However, polyester fibers processed by using the compound are known to generate gases harmful to humans when it combusts, and hence concern has been raised in that its harmfulness to the natural environment is extremely high. In view of the foregoing, various kinds of flame retardant components that replace the halogen compound have been studied, and it has heretofore been found that a phosphorus compounds show good flame retardancy (Patent Literature 1).
A flame retarding method for a polyester fiber in the case where HBCD is used as a flame retardant has involved adhering a flame retardant component to the inside of the fiber in a dyeing bath or according to a thermosol method (continuous dyeing method involving padding the fiber with a dye liquor, drying the resultant, and subjecting the dried product to a dry-heat treatment at high temperature). In contrast, in the case where the phosphorus compound is used, for example, the following processing methods are frequently employed (Patent Literature 2 and 3). The flame retardant is dissolved in a solvent or the like, and the flame retardant component is adhered onto the fiber by immersing the fiber in the solution. Alternatively, the flame retardant is emulsified and dispersed in at least one nonionic surfactant or anionic surfactant, and the flame retardant component is adhered onto the fiber by immersing the fiber in the dispersion simultaneously with its dyeing.
A trend toward the use of phosphorus compounds having higher safety as a flame retardant component for fibers instead of HBCD has been steadily progressing, but there still remain many problems. This is because of the following reasons. When the fiber is processed by the method involving dissolving the flame retardant in a solvent or the like, the solvent or a waste liquid is discharged to the atmosphere, and hence concern about the load on the environment is raised. In addition, when the method involving the use of at least one nonionic surfactant or anionic surfactant is employed, a flame retarding effect is observed, but the amount of flame retardant component adhered onto the fiber is not sufficient, and hence the durable flame retardancy of the fiber is liable to be insufficient. In order to continue to obtain a fiber having a flame retardant effect better than the currently available, the development and improvement of flame retardant compositions having such properties that a flame retardant component adheres in large amounts to fibers have been strongly desired.